This invention relates to a normally open valve that resides totally within a closed vessel containing a liquid, vapor, or gas; and can be closed from the outside of the vessel to isolate the product within from such exterior fixtures as a safety pressure relief valve in the event that the exterior fixture develops an uncontrollable leak.
The valve within the vessel, after being closed will remain closed unless the pressure within the vessel rises to a dangerously high level, threatening to burst the vessel, then it will open spontaneously, releasing the contents of the vessel to the safety pressure relief valve. This will allow the safety pressure relief valve to function normally allowing a small part of the product in the vessel to escape, reducing the internal pressure in the vessel and avoiding its rupturing and avoiding loss of all of the product.
When the pressure within the vessel is returned to a safe level, and the safety pressure relief valve has reclosed, but the original leaking problem of the safety pressure relief valve has not been corrected yet, the normally open valve of this invention that resides totally within the closed vessel may be reclosed again and cyclically function as before as the pressure within the vessel rises again.